85 research outputs found
Using models of the Earth's atmosphere to assess exoplanet habitability
Recent advances in telescope technology have allowed us to detect planets and bodies
that have the potential to be habitable. Habitability can be defined in a number
of ways, but most commonly it is defined by the availability of liquid water. There
are a vast number of factors that determine whether or not liquid water is present
in an atmosphere or on a surface, and due to the limited observational data, our
understanding of the role of each of these factors is poor, especially as we move further
through the parameter space away from the Earth.
Until data from the next generation of telescopes are available, attempts to
constrain atmospheric habitability have to utilise computer modelling. Modelling has
a long history in habitability studies, particularly with regards to the inner and outer
boundaries of the circumstellar habitable zone (CHZ). Early models were 1-dimensional
(1D), but in the last decade the balance has shifted towards 3-dimensional (3D) global
circulation models (GCMs) that describe the air flow in a planetary atmosphere in a
much more sophisticated way. In part this was due to the recognition of the importance
of 3D processes like clouds and convection in the global energy balance, and in part due
to the increasing prioritisation of planets that are dissimilar to Earth, such as M-dwarf
planets, which show features such as tidal-locking and atmospheric jets that result in
less spatial uniformity through the atmosphere, limiting the applicability of 1D models.
As of this writing our current best hopes for habitability are M-dwarf planets such
as the TRAPPIST planets and Proxima Centauri b that orbit in the habitable zone,
with rocky compositions. M-dwarf planets were previously overlooked as candidate
habitable planets in favour of G-star planets like the Earth. However, some researchers
now favour M-dwarfs in light of modern GCM results, observational biases and
planetary population statistics, demonstrating that we must be careful not to define
habitability in a way that is too Earth-centric.
In this thesis we expand on knowledge of habitability through models that are
informed by Earth science, but that do not necessarily describe Earth-like environments.
In Chapter 2, we consider an environment that has not been studied through the lens of
habitability before: ultra-cool Y dwarf atmospheres. In the atmospheres of these bodies
it is thought that there may be liquid water clouds and temperatures and pressures
similar to those on the Earth's surface. However, as there is no surface it is important
that any potential organisms are able to remain above the hot lower atmosphere and
the cold upper atmosphere; we compare with the Earth's atmosphere, where microbes
are able to stay in the atmosphere for weeks, even metabolising in clouds. We study this
environment through a simple radiative or convective atmosphere paired with a model
informed by nutrient-phytoplankton-zooplankton models from the Earth's ocean. We
find that organisms similar in size to microbes can remain aloft in this environment
due to upward convective winds.
In Chapter 3, contrasting with the simple approach in the previous chapter, we
describe the development of a highly-sophisticated, fully online, 3D photochemical
model of an exoplanet atmosphere. We apply this model to a tidally-locked M-dwarf
aqua planet with an Earth-like atmosphere, nominally Proxima Centauri b, to evaluate
the impacts of the differing stellar energy spectrum and dramatically different global
circulation on an ozone layer described through the Chapman mechanism and the
hydrogen oxide catalytic cycle. We find that the ozone layer is unlike that seen in
the Earth's atmosphere. The lack of UV photons from our quiescent M-dwarf results
in very long chemical lifetimes, which means that the atmospheric transport becomes
the dominant factor in the structure of the ozone layer. We see an accumulation of
ozone in the night-side cold traps (or gyres) at low altitudes where transport is slow
and lifetimes are long, resulting in a dramatic day-night contrast in ozone columns.
Total ozone column is much smaller on an M-dwarf planet compared with the Earth,
by around a factor of 10, owing to top-of-atmosphere UV flux.
In Chapter 4, we develop on the results of Chapter 3 by altering certain parameters
in the model and examining the effect on the climate. We find that dramatic changes
occur when switching off the chemistry scheme and reverting to a prescribed Earth
ozone layer. Specifically we find that the temperatures on the night side of the planet
change by more than 50 K, accompanied by dramatic changes in the pole temperatures.
In addition the cold traps move towards the equator and eastwards. These changes are
caused by the smaller ozone columns that result from the interactive chemistry, which
severely reduce night side atmosphere opacity. This opacity controls the night side
cooling rate which in turn controls the atmospheric circulation through the day-tonight
temperature contrast. We find that similar effects occur when switching off the
hydrogen oxide catalytic loss cycle, though to a lesser extent.
Furthermore, we examine the effects of electromagnetic flares on the chemistry,
which do not seem to impact ozone columns, in agreement with previous works. Finally
we demonstrate the changes in atmospheric ozone and climate in a 3:2 resonant orbit
and with an Earth-like orbit and top-of-atmosphere flux. In sum, our results with this
model show that the climate is highly sensitive to the ozone columns, and demonstrate
the importance of fully-coupled 3D photochemical models, which have been used very
rarely in exoplanet atmosphere modelling
Resistance of Antarctic black fungi and cryptoendolithic communities to simulated space and Martian conditions
Dried colonies of the Antarctic rock-inhabiting meristematic fungi
Cryomyces antarcticus CCFEE 515, CCFEE 534 and C. minteri
CCFEE 5187, as well as fragments of rocks colonized by the Antarctic
cryptoendolithic community, were exposed to a set of ground-based experiment
verification tests (EVTs) at the German Aerospace Center (DLR, Köln,
Germany). These were carried out to test the tolerance of these organisms in
view of their possible exposure to space conditions outside of the
International Space Station (ISS). Tests included single or combined simulated
space and Martian conditions. Responses were analysed both by cultural and
microscopic methods. Thereby, colony formation capacities were measured and
the cellular viability was assessed using live/dead dyes FUN 1 and SYTOX
Green. The results clearly suggest a general good resistance of all the
samples investigated. C. minteri CCFEE 5187, C. antarcticus
CCFEE 515 and colonized rocks were selected as suitable candidates to
withstand space flight and long-term permanence in space on the ISS in the
framework of the LIchens and Fungi Experiments (LIFE programme, European Space
Agency)
GIS-DRIVEN ANALYSES OF REMOTELY SENSED DATA FOR QUALITY ASSESSMENT OF EXISTING LAND COVER CLASSIFICATION
Automatization of processes for revision and updating existing GIS information is essential for the modern maintenance of spatial databases. The integration of remotely sensed multi-spectral data into the process of database revision is affected here by the implementation of GIS-driven analyses. The adoption of the GIS-driven principles, provide also an accurate geographical basis for a future supervised classification of the spectral data. The goal of the present research was to define and develop an automatic quality assessment method for the Land Cover classification layer of the Israeli National GIS database. During the experiments on multi-spectral remotely sensed data, effort was carried out in attempt to define "typical " spectral ranges as statistical maximum-likelihood criteria for the classification of each of the land cover phenomenon. These ranges were envisaged to characterize each of the land cover classification groups and to provide quantitative criteria for the definition of various groups of land cover type-classes. The definition of a typical-spectral-variance was executed on the basis of visual, multi-spectral and index bands of remotely sensed data. The decision whether existing GIS classification match the new image reality was made by statistical criteria of maximum likelihood for each investigated land cover type, according to the results of each and every spectral band. The study was based on multi-spectral data of the CASI airborn
Mountain permafrost on active volcanoes: field data and statistical mapping, Klyuchevskaya volcano group, Kamchatka, Russia
Permafrost is widespread in mountainous volcanic areas of the Kamchatka Peninsula. In this paper, we describe geocryological conditions (active layer depths, permafrost temperatures, ground thermal properties and cryostratigraphy) in the Klyuchevskaya volcano group and estimate the spatial distribution of permafrost using a simple statistical model. Measured mean annual ground temperatures (MAGTs) vary from near 08C around 950 m a.s.l. to 78C at 2500 m a.s.l. and permafrost is predicted to occur at elevations > 700 m a.s.l. Heat transfer modelling indicates that the maximum permafrost thickness is about 1000 m for the highest summits (5000 m a.s.l.)
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